JPS5851052A - Control device for thermal expansion of ball screw - Google Patents

Abstract

PURPOSE:To prevent error due to thermal expansion of a ball screw by furnishing a heat emitting member for heating of the ball screw and a temperature control device for this heat emitting member and thereby controlling the temperature of the ball screw. CONSTITUTION:A temp. sensor 5 is buried in a ball nut 3 in engagement with a hollow ball screw 2 to be driven for rotation. The oil in an oil tank 11 being heated by a heater 10 is introduced in an oil hole 8 provided in the ball screw 2 by the hydraulic circuit 12 to heat the ball screw 2. The temperature of the ball screw 2 is sensed by said temp. sensor 5, and the heater 10 is On/Off controlled so that the sensed temperature is slightly higher than the possible maximum temp. rise without temp. control determined through a previous experiment. Thus the rising time before stabilization to the set temperature can be shortened and the variation of once stabilized temp. held minimum, to ensure that the lead error because of thermal expansion of the ball screw can be calibrated easily.

Description

[Detailed Description of the Invention] When used as a feed screw of a machine tool, such as a ball screw, in which a conventional screw shaft and a pole nut are screwed together through a series of balls, with the recent increase in speed and precision, [the Thermal expansion of ball screws has been viewed as a problem. For example, length s oom7
If the temperature of a ball screw of m is increased by just 1℃, the temperature will increase by 0.01.
mm thermal expansion, so even a temperature difference of l'C is a problem that cannot be overlooked in a numerically controlled grinding machine with a minimum setting unit of 0.005 mm. In order to solve this problem, conventional methods have focused exclusively on cooling. However, cooling has poor thermal efficiency, cooling water supply equipment is large and expensive, and small temperature differences (1
It is extremely difficult to control the temperature difference below ℃ by cooling, and it also has a great negative effect on the lubrication management of the ball screw, which in turn impedes the normal function and life of the ball screw. Ta.

The present invention aims to eliminate these conventional drawbacks, and provides a device that controls thermal expansion at low cost, easily, and with high precision by ceasing conventional cooling and instead heating to balance the heat radiation. The purpose is to provide

Examples will be described below.

FIG. 1 shows an embodiment of the apparatus of the present invention. In the figure, the symbol l
is a ball screw, and an oil container 8 penetrates through the center of the screw shaft 2 and the ball screw shaft 2, and both ends of the core oil container 8 are covered with blind plugs 9 and 9'. Reference numeral 10 denotes an immersion heater which heats the oil in the oil tank 11, and the heated oil is introduced into the oil tank 8 by the low pressure hydraulic circuit means 12 and circulated to heat the screw shaft 2. The rising temperature is detected by the eight temperature sensing portions 6 of the temperature detector 5, and is electrically transmitted to the input heater IOK to control ON/OFF of the heater so as to maintain the heat balance between heat radiation and radiation. Temperature sensor number 5: For example, if you use Kusano Kagaku Kikai Seisakusho = 6a Tempcon, control within ±0.01°C is possible, but in reality, control within ±0.2°C is not practical. do not have. The adjustment can be made with the dial 7 (FIG. 2).

FIG. 3 shows another embodiment of the device of the present invention, in which a sheathed heater 13 is fitted around the outer periphery of a ball nut 3.

Reference numeral 14 indicates a heating element embedded in the sheathed heater 13. In this case, heating oil is introduced into the circulation tube 15 by the above-described means, such as by embedding it in the groove 16 screwed on the outer periphery of the heating oil pipe 3 and wrapping it around the ball neck 3. Other embodiments are also shown that provide temperature control. Reference numeral 17 denotes a heat insulating cover that covers the outer periphery of the ball nut 3 in which the circulation tube 15 is embedded.

Figure 5 is a diagram showing the temperature rise of the ball screw during operation.The dotted line is the temperature rise curve of the ball screw due to ball circulation frictional heat in the case of no control, and the solid line shows the temperature rise slightly higher than the above temperature. When heating is controlled by the device of the present invention, the chain line shows the general situation when relying on conventional cooling.

As shown in this figure, according to the device of the present invention, the rise time until the temperature of the ball screw stabilizes at a set temperature slightly higher than the maximum temperature increase when no control is applied is not directly affected by changes in field crops. . Therefore, not only can lead errors caused by thermal expansion of the ball screw be easily calibrated, but the life of the ball screw will not be adversely affected. Furthermore, the device itself has advantages such as being small, inexpensive, and easy to service for users.

[Brief explanation of the drawing]

FIG. 1 is an assembly diagram of a ball screw device showing an embodiment of the present invention;
Figure 2 is an enlarged sectional view showing how the temperature sensor is buried, Figure 3
4 is a partial assembly diagram showing another embodiment of the device of the present invention, and FIG. 5 is a diagram showing the temperature rise of the ball screw. Explanation of symbols 1: Ball screw, 2: Screw shaft, 3: Ball nut, 5:
Temperature detector, 10; Immersion heater, 13: Sealing heater -
15: Circulation tube, 17: Heat insulation cover Patent applicant: NSK Co., Ltd. 2 Figure S 3 Figure

Claims (4)

[Claims] (1) In a ball screw in which a screw shaft and a ball nut are screwed together through a series of balls, a heating element that heats the ball screw and a temperature detector that measures the temperature increase and degree of heating of the ball screw are used. , a means for controlling the temperature of the heating element is provided so that the heating temperature of the ball screw is slightly higher than the maximum temperature rise when no control is performed, which is experimentally determined in advance for the ball screw. A ball screw thermal expansion control device characterized by controlling heating. (2) The thermal expansion control device for a ball screw according to claim 1, which uses heated oil circulating means for introducing heated oil into an oil hole drilled in the axial direction in the screw shaft of the ball screw as the heating element. . (3) The thermal expansion control device for a ball screw according to claim 1, wherein the heating element is a sheathed heater fitted around the outer periphery of a pole nut of the ball screw. (4) The thermal expansion control device for a ball screw according to claim 1, further comprising means for circulating heated oil around the outer periphery of the pole nut as a heating element.